We propose to provide definitive proof of the presence of 26- hydroxycholesterol and 24-hydroxycholesterol (and other similar oxidized cholesterol derivatives) in human blood and to develop analytical procedures for the measurement of these sterols in human plasma. We propose to develop two assay procedures, one involving gas chromatography-mass spectrometry, the other involving radioimmunoassay, and to compare plasma 26-hydroxycholesterol levels as measured by the two techniques. With either or perhaps both methods we will undertake broad screening of human blood samples from volunteers and from patients with diagnosed cardiovascular disorders, especially atherosclerosis, hyperlipidemia, hypertension, obesity, etc. in order to attempt to correlate plasma sterol levels with the medical disorder. Use of the analytical approach for the prediction of developing cardiovascular disorders will be evaluated, and the possibility of broad clinical application of the methods will be examined. Additionally the tissues in which 26-hydroxycholesterol is biosynthesized from cholesterol will be sought in order that a fully more fundamental understanding of the relationships between 26-hydroxycholesterol and human atherosclerosis may be had.